The purpose of this project is to understand better the development of the endometrium and oocyte in women and to investigate the role of gonadal steroids in the processes. Progesterone is essential for the normal morphologic development of the luteal phase endometrium, and for maintenance of pregnancy. While relative deficiency of progesterone has been implicated in infertility and early pregnancy loss, there is no accurate non-invasive test for this. We have previously shown little correlation between endometrial maturation and serum levels of progesterone or a progestin-dependent glycoprotein, placental protein 14 (PP14). We thus evaluated the ability of exogenous hCG to stimulate consistently progesterone and PP14, so as to develop a new test for luteal function. The finding that 26 normally cycling women had progesterone levels> 11 ng/mL at 6 hours after hCG administration, suggests that this approach deserves further testing in a group of women with abnormal endometrial biopsies. Our studies suggest that growth hormone (GH) is an important mediator of follicular development. The GH receptor is present in the granulosa cells of the developing follicle and in the corpus luteum, the estrogen and progesterone steroidogenic compartments. We also demonstrated that a complete fast for 72 hours during the mid-follicular phase does not disrupt folliculogenesis, ovulation, or menstrual cycle dynamics. The process of uterine remodelling that is so remarkable in the mammalian uterus is achieved through a coordinated proliferation, differentiation and cell death. While the gonadal steroids estradiol and progesterone appear to be required for these organ-specific processes, the mechanism(s) by which these processes are regulated remain unclear. Potential mediators of estrogen action include IGF-1 and c-myc, a transcription factor known to be induced by growth factors, which appears to participate in the regulation of DNA synthesis in other systems. We used a well-characterized in vivo ovariectomized mouse model to correlate sex steroid-induced proliferation with the induction of IGF-1 and c-myc mRNA in the uterine endometrium. We have found that IGF-1 and c-myc levels parallel each other and the estrogen-induced processes of differentiation in this model, suggesting that they are important to proliferation. The induction of IGF- 1 by GH in other tissues prompted an evaluation of whether the GH receptor was present in the endometrium, based on the hypothesis that GH might act directly on the endometrium and so modulate estrogen effect. GH receptor was found to be present throughout the endometrium, but was not regulated by estradiol.